This section is intended to introduce various aspects of the art, which may be associated with embodiments of the disclosed techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the disclosed techniques. Accordingly, it should be understood that this section is to be read in this light, and not necessarily as admissions of prior art.
Volumetric (3D) model construction and visualization have been widely accepted by numerous disciplines as a mechanism for analyzing, communicating, and comprehending complex 3D datasets. Examples of structures that can be subjected to volumetric analysis include the earth's subsurface, facility designs and the human body. The ability to easily interrogate and explore 3D models is one aspect of 3D visualization. Relevant models may contain both 3D volumetric objects and co-located 3D polygonal objects. One example of a volumetric object is a seismic volume, shown in FIG. 1 at reference number 100. Other examples of volumetric objects are seismic volumes, MRI scans, reservoir simulation models, and geologic models. Interpreted horizons, faults and well trajectories are examples of polygonal objects. In some cases, there is a need to view the volumetric and polygonal objects concurrently to understand their geometric and property relations. If every cell of the 3D volumetric object is rendered fully opaque, as is the case with seismic volume 100 in FIG. 1, other objects in the scene may be occluded, and so it becomes advantageous at times to render such volumetric objects with transparency so that other objects may be seen through them. As an example, FIG. 2 depicts seismic volume 100 displayed with a degree of transparency. These 3D model interrogation and exploration tasks are useful during exploration, development and production phases in the oil and gas industry. Similar needs exist in other industries.
3D volumetric objects may be divided into two basic categories: those rendered using structured grids and those rendered using unstructured grids. Other types of grids may be defined on a spectrum between purely structured grids and purely unstructured grids. Both structured and unstructured grids may be rendered for a user to explore and understand the associated data. Known volume rendering techniques for structured grids render a full 3D volume with some degree of transparency, which enables the user to see through the volume. However, determining relations of 3D object properties is difficult, because it is hard to determine the exact location of semi-transparent data.
One way to view and interrogate a 3D volume is to render a cross-section through the 3D volume. The surface of the intersection between the cross-section and the 3-D volume may be rendered as a polygon with texture-mapped volume cell properties added thereto. For a structured grid rendered for a seismic or a medical scan, the user can create cross-sections along one of the primary directions: XY (inline or axial), XZ (cross-line or coronal) and YZ (time slice or sagittal). A traditional cross-section spans the extent of the object. In this case other objects such as horizons, wells or the like are partially or completely occluded and it is difficult to discern 3D relationships between objects. This effect is shown in FIG. 3, which is a 3D graph 300 of a subsurface region. The graph 300, which may provide a visualization of 3D data for a structured grid or an unstructured grid, shows a first cross-section 302, a second cross-section 304, a third cross-section 306, and a fourth cross-section 308. Each of the four cross-sections is chosen to allow a user to see data in a physical property model that comprises data representative of a property of interest. However, a first horizon 310 and a second horizon 312, as well as data displayed on cross-sections 302, 304 and 306 which also may be of interest to a user, are mostly obscured or occluded by the visualizations of the four cross-sections.
A ribbon section is one attempt to make traditional cross-sectional visual representations more flexible. One way to create a ribbon section is to extrude a line or polyline vertically through the volume, creating a curtain or ribbon, upon which surface the volumetric data from the intersection of the ribbon with the volume is painted. This concept of ribbon sections is depicted in FIG. 4, which is a 3D graph 400 of a subsurface region showing a ribbon section 402 defined by a polyline 404 comprising a first line segment 406 and a second line segment 408. Although ribbon section 402 is less intrusive than the cross-sections shown in FIG. 3, portions of a first horizon 410 and a second horizon 412 are still occluded as long as the ribbon section is displayed.
Another attempt to make traditional cross-sectional visual representations more flexible is to implement a three-dimensional probe within the data volume. This is demonstrated in FIG. 5, where a cube-shaped probe 500 is painted with volumetric data from the intersection of each of the probe's surfaces with the volume. Probe 500 may be moved around within the data volume. However, there are still instances in which horizons 502, 504 may be occluded.
All of the above methods rely on predefined geometric primitives like planes, combinations of planes, polylines, volumes, hexahedrons and others. These primitives are simple to understand, but they rarely match the geometry of a physical object. The above methods sometimes provide editing capabilities, like the ability to edit the polyline or change the orientation of the cross-section, so the user may better match the physical object. However, the editing tasks are time consuming and very often a perfect match cannot be obtained e.g. when a curved physical object is examined with a planar cross-section.
U.S. Patent Application Publication No. 2005/0231530 discloses a method for 3D object creation and editing based on 3D volumetric data via 2D drawing tools. In its operation, the user creates a 2D structure in the rendering space. These 2D structures, such as 2D points, 2D lines etc, are transformed/projected into 3D structure. This method relies on visualization of the 3D volumetric data as well as 2D interactions happening in the same rendering space. By doing this, the user's 2D operations are restricted by how the 3D data is visualized in rendering space. For example, their rendering of volumetric data uses planar slices (also known as cross-sections), and the 3D structures created by the 2D drawing tools will be collocated with these planar slices. To create a non planar 3D structure the user must perform digitization on numerous planar slices. For example, creating a cylinder requires drawing circles on a large number of 2D slices intersecting the cylinder. Another example involves creating a curved surface connecting two vertical wells. The method disclosed in the '530 Application requires a user to digitize lines on multiple time slices. What is needed is a method of rendering or displaying data using simple, intuitive editing commands while minimizing occlusion of data of interest.